<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
            canvas{
                border:1px solid black;
            }
        </style>
</head>
<body>
        <canvas width=600 height=400 id="cas"></canvas>
        <script>
        var cas = document.getElementById("cas");
        var ctx = cas.getContext("2d")
        // ctx.arc(100,100,50,0,Math.pI);
        // ctx.fill(); 
         function toAngle (radian){
             return radian * 180 /Math.PI;
         }
         function toRadian (angle){
             return angle * Math.PI / 180;
         }

        </script>
</body>
</html>